Heretofore, in the medical and printing plate making fields, effluent resulting from wet type processing for image forming materials became problematic in terms of workability, and in recent years, from the viewpoint of environmental protection as well as space saving, a decrease in processing effluent has been highly demanded. Accordingly, a silver salt photothermographic dry imaging material, which can perform image formation only by heating, has been brought into practical use and rapidly prevailing in the above fields.
A photothermographic dry imaging material itself has been proposed for a long time (for example, please refer to Patent Documents 1 and 2). This silver salt photothermographic dry imaging material is generally processed with a thermal development processor, which forms images by applying stable heat to said material and is called as a laser imager. As described above, a great number of laser imagers have been supplied on the market in accordance with rapid pervasion in recent years. Further, in recent years, improvements for more compact size and more rapid processing of laser imagers are required.
Therefore, improvement of characteristics of photothermographic dry imaging material is indispensable. To obtain sufficient density of a photographic image even with rapid processing, it is effective to increase covering power by increasing coloring points by use of silver halide grains having a small mean grain size (for example, refer to Patent Documents 3 and 4), to utilize a highly reactive reducing agent provided with a secondary or tertiary alkyl group (for example, refer to Patent Document 5), or to utilize a development accelerator such as phenol derivatives and naphthol derivatives (for example, refer to such as Patent Documents 6 and 7). Further, in a photothermographic dry imaging material utilizing photosensitive silver halide grains, there is a problem of deterioration of light irradiation image lasting quality (storage stability when an image obtained by thermal development is used in a daylight room for such as diagnosis or stored in a daylight room) because of remaining silver halide grains in a photosensitive layer even after thermal development, and it has been tried to solve this problem (for example, refer to Patent Documents 8 and 9).
Further, disclosed is a thermal development apparatus which develops a film, on which a latent image has been formed, by heating a silver salt photothermographic dry imaging material from the EC surface (the emulsion surface) while being slid between a heating drum and a plural number of opposing rollers (for example, refer to Patent Document 10). Disclosed is a thermal development apparatus in which a fixed heater divided into three parts is utilized instead of the foregoing heating drum, the BC surface side (the substrate surface side) of a film is heated while being slid on said heater (for example, refer to Patent Document 11). In conventional thermal development apparatuses, thermal development time was generally approximately 14 seconds (a length in the transportation direction of 17 inches), and further speed up of a thermal development process is required. However, in these Patent Documents, measures for rapid thermal development are neither indicated nor disclosed. As measures for rapid processing from the apparatus aspect, disclosed are techniques such as to perform thermal development while transporting a film at not less than 23 mm/sec, and to perform thermal development simultaneous with exposure (for example, refer to Patent Documents 12 and 13). However, since a distance between an exposure section and a development section is short, low molecular weight components in a thermally developable photosensitive material, which are generated from a film by thermal development, will influence to as far as the exposure section, which results in a problem of generating contamination of an exposure apparatus; and attempts have been tried to solve this problem (for example, refer to Patent Documents 14 and 15).                [Patent Document 1] U.S. Pat. No. 3,152,904        [Patent Document 2] U.S. Pat. No. 3,457,075        [Patent Document 3] JP-A 11-295844 (hereinafter, JP-A refers to Unexamined Japanese Patent Publication No.)        [Patent Document 4] JP-A 11-352627        [Patent Document 5] JP-A 2001-209145        [Patent Document 6] JP-A 2002-006443        [Patent Document 7] JP-A 2003-066558        [Patent Document 8] JP-A 2003-270755        [Patent Document 9] JP-A 2004-004522        [Patent Document 10] Japanese Translation of PCT International Application Publication No. 10-500497        [Patent Document 11] JP-A 2003-287862        [Patent Document 12] US Patent Application Publication No. 2004/58,281        [Patent Document 13] JP-A 2004-085763        [Patent Document 14] JP-A 2002-162692        [Patent Document 15] JP-A 2004-085763        